Apnea is the cessation of breathing. Sleep apnea is the cessation of breathing during sleep. Sleep apnea is a common sleep disorder that affects over twelve million (12,000,000) people in the United States. Persons with sleep apnea may stop and start breathing several times an hour while sleeping. Each individual episode of the cessation of breathing is referred to as a sleep apnea event.
When a person stops breathing during sleep the person's brain soon senses that oxygen levels in the blood are low and carbon dioxide levels in the blood are high. The brain then sends emergency signals to the body to cause the body to try to increase gas exchange in the lungs to increase the amount of oxygen and to decrease the amount of carbon dioxide. The body's autonomic physiological reflexes initiate survival reactions such as gasping for air, the production of enzymes to constrict arteries to increase blood pressure, and the production of enzymes to increase heart rate. The person will then usually gasp for air and thereby restore the effective gas exchange of oxygen and carbon dioxide in the lungs. This causes the sleep apnea event to end.
The brain may also cause the body's autonomic physiological reflexes to release large amounts of adrenaline in order to stir the person to gasp for air. Over a period of time repeated rushes of adrenaline in the body can have negative effects and can lead to heart damage and other medical problems.
Often the person wakes up while gasping for air. Even if the person does not become conscious while gasping for air, the body's sleep state is interrupted and the body is physiologically stressed during each sleep apnea event. Sleep apnea events can occur multiple times during a period of sleep. That is, the process of ceasing to breathe, become physiologically stressed, and gasping for air may be repeated numerous times during a period of sleep. Successive sleep apnea events cause a person to experience many short interrupted periods of sleep.
Interrupted periods of sleep can produce varying levels of fatigue, lack of energy, and daytime sleepiness. Other symptoms may include restless sleep, loud and sometimes heavy snoring, morning headaches, irritability, mood changes, behavior changes, and similar emotional or physical disorders. While mild forms of sleep apnea may exist without apparent harm to the individual, severe cases may lead to such conditions as weight gain, impotency, high blood pressure, stroke, mental problems, memory loss, and even death.
Sometimes sleep apnea directly causes death during sleep due to asphyxiation because of a lack of oxygen. More frequently sleep apnea indirectly causes death because of motor vehicle crashes, job-site accidents, and similar events which are due to sleepiness caused by sleep deprivation.
There are two forms of sleep apnea. The two forms are central sleep apnea and obstructive sleep apnea. At the present time, central sleep apnea and obstructive sleep apnea are thought to originate from two different sources. Central sleep apnea appears to be linked to a malfunction of the brain that interferes with neurological signals that normally control the breathing process. Obstructive sleep apnea is caused by a blockage of the breathing airway that completely stops the flow of air to and from the lungs. A common form of obstructive sleep apnea occurs when fleshy tissue in a sleeping person's throat collapses and seals off the pharyngeal airway. A condition called mixed sleep apnea results when central sleep apnea events and obstructive sleep apnea events alternate.
Sometimes central sleep apnea directly causes death during sleep when the sleeping person completely ceases breathing. Death results from asphyxiation due toga lack of oxygen. More frequently obstructive sleep apnea indirectly causes death because of motor vehicle crashes, job-site accidents, and similar events that are due to sleepiness caused by sleep deprivation.
Because of the variety and degree of symptoms, diagnosis of obstructive sleep apnea typically requires more than a simple analysis of symptoms. Depending upon the symptoms and severity, diagnosis may include a thorough physical exam, an examination of the mouth and throat for abnormalities, and sleep studies. Thorough sleep studies include additional tests such as electrocardiogram (ECG) tests for detecting arrhythmias, and tests for arterial blood gases to find sleep periods in which the blood oxygen level is below its normal low level.
Successful treatment for obstructive sleep apnea must ensure that a person's breathing passages remain open during sleep. The simplest treatments include weight reduction, change in body position while sleeping, avoidance of alcohol, avoidance of sedatives, and similar changes in lifestyle. When anatomical obstructions are found to be the source of obstructive sleep apnea, surgery may be required for removal of enlarged tonsils, enlarged adenoids, excess tissue at the back of the throat, and similar types of obstructions. In more extreme cases, an opening may be created in the trachea in order to bypass the obstruction that is blocking the airway during sleep.
One device for the treatment of obstructive sleep apnea is a device that pumps fresh air into a mask worn over the nose. This device provides what is known as nasal continuous positive airway pressure (CPAP). When the mask and air flow are properly adjusted, the air pressure opens the upper air passage enough to prevent snoring and known forms of apnea. The disadvantages of the CPAP treatment include 1) discomfort and sleep disruption caused by the nose mask and the mechanism for connecting the mask to the air pumping device, and 2) original and on-going cost for the apparatus, and 3) inconvenience when the sleeping location changes. Some newer types of CPAP devices do not use a mask (e.g., the CPAP device disclosed in U.S. Pat. No. 6,012,455).
In addition to the more traditional treatments for obstructive sleep apnea described above, alternatives are constantly being studied and developed. Medications are being researched, but no medication has yet been developed which has proven to be effective. Mechanical devices that are inserted into the mouth while sleeping have been tried with varying success. For instance, devices which keep the jaw or tongue in proper position are sometimes effective in cases where breathing is obstructed by a large tongue or a “set back” jaw. However, these devices have some disadvantages. They are uncomfortable to wear during sleep (which causes them to not be regularly used). Each device must have a different design for each specific type of air passage obstruction. Each device must be individually sized for each patient.
More recently, systems have been developed for the purpose of clearing upper airway passages during sleep using the electrical stimulation of nerves or muscles. In some cases, these systems require surgical implantation of sensors and associated electronics that detect when breathing has ceased and then stimulate the breathing process. Some hybrid systems have been developed that require surgical insertion of one or more sensors plus external equipment for monitoring the breathing process or moving the obstruction when breathing ceases. These systems may produce positive results but they also have associated risks due to surgery, may need replacement at later times (requiring additional surgery), and may have higher costs and lower reliability than the more traditional treatments. In addition, the hybrid systems also have the accompanying physical restrictions and accompanying disadvantages associated with connections to the external equipment.
Therefore, there is a need in the art for an improved system and method for treating obstructive sleep apnea. In particular, there is a need in the art for a system and method that does not create other types of sleep disturbing effects, does not require surgical implementation, and does not have the high costs associated with some of the types of treatments currently in use.
Prior art systems and methods are directed toward detecting and treating an obstructive sleep apnea event after the obstructive sleep apnea event has occurred. It would be very advantageous, however, to be able to detect the onset of an obstructive sleep apnea event before the obstructive sleep apnea event fully develops. That is, if the onset of an obstructive sleep apnea event can be detected before the sleeping patient actually stops breathing, steps can be taken to prevent the obstructive sleep apnea event from occurring.
Therefore, there is a need for a system and method for detecting the onset of an obstructive sleep apnea event before the obstructive sleep apnea event fully develops. In particular, there is a need for a system and method for detecting the onset of an obstructive sleep apnea event before the cessation of breathing occurs.